1. The Field of the Invention
The present invention relates to manufacturing optical transceivers and coupling elements. More particularly, the present invention relates to systems and methods for manufacturing optical coupling elements in transceivers with multiple ports.
2. The Relevant Technology
Communication over optical fiber networks utilizes light signals that are effectively trapped inside of optical fibers. Because the light signals are trapped within a particular fiber, many fibers can be included in a single cable without concern about interference from the light signals carried by nearby fibers. Optical fibers also have the property of strongly rejecting interference that would otherwise be caused by radio frequencies and electromagnetic radiation. These characteristics make fiber optics ideally suited for many applications.
In order to transmit light signals using optical fibers, it is first necessary to introduce light into the fibers. Exemplary sources of light used in fiber optics are light emitting diodes and laser diodes. Coupling the light to a fiber, however, is not always efficient because the numerical aperture of the fiber is typically smaller than the common laser diode sources. Thus, coupling optics are needed for effective conversion of the laser diode mode to the transmitted optical mode inside the single mode optical fiber. Because coupling optics also have transmission losses and aberrations, only a portion of the light emitted by a light source that satisfies the physical characteristics of the transmitted fiber mode is effectively transmitted through the coupling optics and effectively coupled with the optical fiber. In addition, the power consumed by the light source is often increased in order to ensure that the light signal transmitted through the optical fiber has sufficient transmission power. To overcome these losses, the light sources are typically coupled or connected with optical fibers using high optical quality coupling elements with efficient anti-reflection coatings. This has the effect of reducing the power consumed by the light source while directing more light into the optical fiber. In addition to coupling a light source to an optic fiber, coupling elements are also used to couple or connect one optical fiber to another optical fiber and to couple or connect an optical fiber to a light detector.
Typical coupling elements or transceiver ports typically use ball lenses, aspheric lenses or graded index (GRIN) lenses. Ball lenses are significantly less expensive than aspheric lenses and GRIN lenses because they are simple to manufacture. However, the performance of GRIN lenses and aspheric lenses is significantly better than the performance of ball lenses.
A typical ball lens used to couple a laser diode output to a single mode fiber shows diffraction limited performance only in the 0.15 numerical aperture (A) region of the optical source. The same ball lens, when used to couple a single mode fiber to another single mode fiber can only couple light effectively up to 0.11 NA of the input fiber. Higher NA light output from the laser diode or the single mode fiber is highly aberrated and does not couple effectively when using coupling elements that include ball lenses.
GRIN lenses and aspheric lenses, on the other hand, perform significantly better than typical ball lenses. Laser diodes with beam divergence angles in the 0.5 NA region can effectively be coupled into single mode fibers using appropriate aspheric lenses. Unfortunately, the lowest cost aspheric glass lenses are significantly more expensive than ball lenses.
The advantage of using GRIN lenses or aspheric lenses over ball lenses is that a fiber optic system can generate sufficient transmission power with minimum laser output for any given link. In addition, low aberration imaging of the fiber output onto small detectors permits effective capture of the transmitted light when using GRIN lenses or aspheric lenses. The disadvantage of using GRIN lenses or aspheric lenses is their cost. Currently, low cost aspheric lenses are 10 to 20 times more expensive than ball lenses. What is needed are systems and methods of manufacturing low cost, high efficiency coupling elements or ports that provide improved optical performance.